1. Field of the Invention
This invention relates to small air-powered vacuum sources and, more particularly, to an airflow-type vacuum inducing unit which is quiet in operation and safe to use in an environment where electrostatic discharges cannot be tolerated.
2. Description of the Related Art
There has long been a need in the microelectronics industry for a small vacuum generator that can be used conveniently to clean hard-to-reach places and to manipulate fragile miniature components such as microchips. An additional requirement is that such a device can be used in a cleanroom environment. Also, it is often necessary that the device be used under circumstances in which the generation of any kind of electrostatic charge is unacceptable. The types of vacuum cleaners which are known generally fail to provide these desirable features in combination. Moreover, such vacuum cleaners as are generally used in electronic assembly areas to remove contamination and debris during manual handling operations of circuit boards, electronic assemblies and the like are generally noisy and somewhat ineffective. Other small vacuum cleaners which have become popular with the advent of personal computers and are principally designed to withdraw dust, hair and lint from computer keyboards are simply too lightweight and low powered to be effective in a shop or electronic assembly line environment in serving the present need. Apparatus of the present invention avoids the drawbacks associated with conventional vacuum cleaners by using a quieter source of power and a principle of operation without reliance on motors or other moving parts. Embodiments in accordance with the present invention utilize the venturi principle to develop reduced pressure in a tube from the flow of high velocity air across the tube. Such a device may be considered a vacuum generator and is used to develop the vacuum which is employed in the present invention.
Some examples of prior art related to tools which use a vacuum produced by airflow include the following:
U.S. Pat. No. 1,334,430 to Ayotte relates to dust collectors for drills and in particular to a means for collecting dust and particles created by the drill so as to prevent the same from mingling with the air in a mine and affecting the health of the miners. A tubular casing is adapted to surround a drill bit and receive the dust and rock particles thrown off by the bit. The casing is connected to the bent end of a pipe which extends parallel with the drill bit and has its other end connected with the bent end of a second pipe which communicates with a detachably secured dust collecting bag. Suction in the casing is created by the flow of compressed air through a nozzle extending into the end of the second pipe. Dust created by the drill passes with the air coming from the nozzle through the second pipe into the collecting bag. The air passes through the meshes of the fabric of the bag while the dust is caught and held by the bag.
U.S. Pat. No. 1,802,920 to Lee is directed to a device for cleaning molds and patterns or the like. A hollow body member is provided with a tube connected to the bottom of the hollow body member. A valve-controlled air inlet is provided on the device which is connected to a supply of air under pressure by means of a flexible conduit. One end of the hollow body member is open and provided with a closure member which may be hinged to the body member but is normally held open by a spring. The tool is operated by inserting the tube in a mold, for example, and operating the valve to permit air flow through the hollow body member to create a suction which sets up a flow of air through the tube. The tube can be manipulated within the mold to remove dirt or other extraneous matter by means of the suction created.
U.S. Pat. No. 1,986,476 to Ironside relates to a device for transferring liquids between different containers, in particular heavy oils and fluid greases. A relatively small and portable closed tank is provided which has a top wall through and from which a conduit extends. The conduit end within the tank cavity is disposed adjacent to the bottom of the cavity while a flexible hose of required length is coupled to the outer conduit end. If a sub-atmospheric pressure is created in the tank cavity while the free end of the hose is immersed in a liquid, the liquid is drawn into the tank through the hose so long as the sub-atmospheric pressure obtains. On the other hand, if the tank contains liquid above the bottom end of the conduit and a pressure exceeding atmospheric is created in the tank, the liquid is forced from the tank through the conduit and hose so long as the conduit end is immersed and the pressure exceeds that of the atmosphere. Means for providing the desired pressure conditions in the tank comprise an air compressor and a control means connected between the tank and a hose from the compressor. The control means comprises a body through which an air passage extends longitudinally, and the passage is divided to define two portions by means of a nozzle disposed therein. Mounted in one of the passage portions to extend axially therethrough and therefrom is a tubular member with a bore aligned with the nozzle bore whereby air discharged from the nozzle will move freely into the bore. When an airstream under pressure is introduced through the nozzle, its flow through the bore draws air with it from the passage portion so as to create a vacuum therein, with the result that the continued removal of air draws air from the tank cavity.
U.S. Pat. No. 3,525,118 to Viollet discloses a special adaptation of a machine shop blow gun apparatus having vacuum and blow extension members mounted on a standard blow gun so as to be connected with each other and also to a source of a compressed air. The blow gun has a blow extension opening that can be covered so as to direct the compressed air out the end of the member that functioned as a vacuum member before the exhaust member was closed.
U.S. Pat. No. 761,996 to Tell is directed to a pen-shaped suction tool for collecting and keeping small particles and other objects. The suction is generated by an ejector contained in the tool. Suction is started by closing an outflow opening for air under pressure supplied to the tool, which opens a valve through the displacement of a piston. The valve and piston are located in a common cylindrical chamber.
U.S. Pat. No. 3,971,096 to Renholt relates to a pressurized air-driven suction device comprising one or more nozzles for ejecting pressurized air and including appurtenant venturi tubes situated in an elongated tubular ejector housing. If desired, the ejector housing may be provided with a silencer. A suction air pipe for supplying suction air is also mounted in the ejector housing, which is itself mounted through the end plate of a container such as an oil drum having plug holes.
Two examples of prior art related to the elimination of electrostatic discharges are described briefly below.
U.S. Pat. No. 2,426,315 to Marick is directed to a static-free brush produced by depositing upon the bristles thereof a thin electrically conducting coating and making the head in which the bristles are mounted and the brush handle conductive. A static charge at the bristles is conducted to the hand and dispersed over the body of the person using the brush.
U.S. Pat. No. 2,665,443 to Simon et al relates to the reduction or elimination of static electricity from a hairbrush or comb by dipping it in a dilute dispersion of particular chemical substances and then drying it. The substances disclosed are defined as certain long-chain fatty-acid partial esters.
None of the patents described above discloses an air-powered miniature vacuum generator for the cleaning of electronic assemblies or the manipulation of small parts that is extremely quiet in operation, will capture both liquid and particulate contaminants, and not present an electrostatic discharge problem to components.